JP2010161014A - Alkaline storage battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alkaline storage battery capable of preventing occurrence of peeling of an active material even if a conductive core of a low porosity is used and capable of obtaining high output characteristics by reducing reactive resistance. <P>SOLUTION: The alkaline storage battery 10 is provided with a hydrogen storing alloy negative electrode 11 having hydrogen storing alloy as a negative electrode active material and a positive electrode 12 having nickel hydroxide as a main positive electrode active material, and an electrode group spirally wound through a separator 13 separating both the electrodes 11, 12, and alkaline electrolyte solution are housed in an outer can 16. Then, The porosity of the conductive core 11a used in the hydrogen storing alloy negative electrode 11 is 15%-25%, and polytetrafluoroethylene (PTFE) is applied on the surface of the hydrogen storing alloy negative electrode 11 by 0.02 mg/cm<SP>2</SP>-0.11 mg/cm<SP>2</SP>, the holding ratio of the electrolyte solution held by the hydrogen storing alloy negative electrode 11 is 23%-29% against the total electrolyte solution volume. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an alkaline storage battery suitable for an application requiring a large current discharge such as a hybrid vehicle (HEV: Hybrid Electric Vehicle) or an electric vehicle (PEV: Pure Electric Vehicle), and in particular, a hydrogen storage alloy is used as a negative electrode active material. A hydrogen storage alloy negative electrode and a positive electrode having nickel hydroxide as a main positive electrode active material, and an electrode group wound in a spiral shape through a separator separating these two electrodes, and an alkaline electrolyte solution in an outer can The present invention relates to an alkaline storage battery housed in a container and a method for producing the same.

  In recent years, alkaline storage batteries, particularly nickel-hydrogen storage batteries, have come to be used for power sources of vehicles such as hybrid vehicles (HEV) and electric vehicles (PEV). The alkaline storage battery used for this type of application is required to be downsized because a plurality of single cells are connected in series. Here, when the alkaline storage battery is downsized, the facing area between the positive and negative electrodes decreases, so that the normal temperature output characteristics and the low temperature output characteristics deteriorate, and at the same time the miniaturization and high output are achieved. There is a need.

As means for downsizing, there are a method of reducing the cylindrical diameter of the cylindrical battery and a method of shortening the battery height. In this case, in the method of reducing the diameter of the cylinder, when used in a large current application, the current density in the current collector becomes excessive, reaction resistance occurs, and problems such as voltage drop occur. Become. For this reason, a method of shortening the battery height as shown in Patent Document 1 (Japanese Patent Laid-Open No. 11-354150) is desirable.
On the other hand, as shown in Patent Document 2 (Japanese Patent Laid-Open No. 9-31158) and Patent Document 3 (Japanese Patent Laid-Open No. 10-32238), as means for increasing the output, the current collecting property of the conductive core is described. Focusing on the improvement, there is a method of reducing the aperture ratio of the conductive core.

JP 11-354150 A Japanese Patent Laid-Open No. 9-312158 Japanese Patent Laid-Open No. 10-32238

However, it has been found that when the battery height is shortened and a conductive core having a low porosity is used, the output characteristics and the life are reduced.
Therefore, when disassembling and investigating a battery with reduced output characteristics and reduced life, peeling of the active material was observed at the negative electrode end (bottom side of the outer can) of the electrode group wound in a spiral shape. It was. This is because the binding force of a general active material is a covalent bond force, a hydrogen bond force, an electrostatic interaction force, a van der Waals force, etc., and all of them are based on Coulomb force. As is well known, this Coulomb force is expressed by q1 · q2 / (4π · ε · r ² ) and is inversely proportional to the dielectric constant ε. Here, when there is an excessive amount of electrolytic solution having a large dielectric constant at the binding point, it is considered that the binding force of the active material becomes weak and active material peeling occurs.

  In this case, since the bonding strength between the negative electrode active materials is maintained by the Coulomb force (particularly, electrostatic interaction) between the negative electrode active materials in the apertures, the negative electrode using a conductive core having a low porosity In the case, the strength between the active materials tends to decrease. When the spirally wound electrode group is accommodated in the outer can and the electrolyte is injected, the electrolyte follows the inner wall of the outer can and moves to the bottom of the outer can. For this reason, by shortening the battery height, the electrolyte tends to accumulate at the negative electrode end (bottom side of the outer can) of the electrode group wound in a spiral shape, and the electrolyte is temporarily excessive. Will occur.

  As a result, when the battery height is shortened and a conductive core having a low porosity is used, an excessive amount of electrolyte is temporarily generated at the bottom of the outer can, and the negative electrode end (the bottom side of the outer can) ), The electrostatic interaction between the active materials is extremely weakened, the active material is peeled off, the reaction resistance is increased, and the output is decreased. Further, once the active material is peeled off, the excessive state of the electrolytic solution is accelerated, and the distribution of the electrolytic solution is biased. As a result, it is considered that the heat generation due to the heterogeneous reaction accompanying charging / discharging increased, resulting in a decrease in life.

  Therefore, the present invention has been made to solve the above-described problems, and even if a conductive core having a low porosity is used, the active material is prevented from peeling off, and the reaction resistance is reduced. It aims at providing the alkaline storage battery from which a high output characteristic is acquired by this.

The alkaline storage battery of the present invention comprises a hydrogen storage alloy negative electrode using a hydrogen storage alloy as a negative electrode active material, and a positive electrode using nickel hydroxide as a main positive electrode active material, and is spirally arranged through a separator that separates both electrodes. The wound electrode group and the alkaline electrolyte are accommodated in an outer can. And in order to achieve the said objective, the porosity of the electroconductive core used for the hydrogen storage alloy negative electrode ([total area of opening of core body / length of negative electrode x width] x 100) is 15% to 25%, the surface portion of the hydrogen storage alloy negative electrode polytetrafluoroethylene (PTFE) is 0.02mg / cm ² ~0.11mg / cm ² only has been applied, the hydrogen storage alloy negative electrode for the electrolytic solution total held The retention rate of the electrolytic solution is 23% to 29%.

Here, it has been clarified that when the open area ratio of the conductive core is larger than 25%, it is not possible to obtain an output higher than the conventional one. Further, it has been clarified that when the hole area ratio of the conductive core is smaller than 15%, the active material is peeled off during rolling in the electrode plate manufacturing process. In addition, when the amount of PTFE applied is greater than 0.11 mg / cm ² , PTFE becomes a reaction resistance, resulting in a decrease in output, and when it is less than 0.02 mg / cm ^2, it is clear that an output improvement effect cannot be obtained. Became.

Therefore, the conductive core used in the hydrogen storage alloy negative electrode of the present invention has a porosity of 15% to 25%, and PTFE is 0.02 mg / cm ^{2 to} 0 on the surface of the hydrogen storage alloy negative electrode. Only 11 mg / cm ^{2 is} applied. In this case, an electrolytic solution of a hydrogen storage alloy negative electrode when a conductive core having a porosity of 15% to 25% is used and PTFE is applied to the surface portion by 0.02 mg / cm ^{2 to} 0.11 mg / cm ^2. It was revealed that the retention rate was 23 to 29% with respect to the total amount of the electrolytic solution. And, as described above, when the porosity of the conductive core, the amount of PTFE applied, and the electrolyte retention rate are defined, even if an excessive portion of the electrolyte is generated at the bottom of the outer can, The active material peeling of the hydrogen storage alloy negative electrode can be avoided, and the electrolyte can be penetrated into the inside of the hydrogen storage alloy negative electrode wound in a spiral shape. Became possible.

In this case, when the total thickness of the hydrogen storage alloy negative electrode is t1, and the thickness of the conductive core of the hydrogen storage alloy negative electrode is t2, the surface portion of the hydrogen storage alloy negative electrode is more than the surface of the hydrogen storage alloy electrode ( It is within the range of t1-t2) × 0.15. The hydrogen storage alloy used at this time is preferably an alloy containing an A ₅ B ₁₉ type structural phase containing rare earth, nickel and magnesium as main elements. This is because the nickel (Ni) ratio per unit crystal lattice having a catalytic effect can be increased by including the A ₅ B ₁₉ type structural phase, so that the electrolyte retention rate of the hydrogen storage alloy negative electrode is higher than the conventional one. This is because high output characteristics can be obtained within a small range of the present invention.

  As described above, as a manufacturing method for applying PTFE to the surface portion of the hydrogen storage alloy negative electrode, a slurry application step of applying a hydrogen storage alloy slurry to a conductive core to form a slurry-coated electrode plate; A drying step of drying the slurry-coated electrode plate to form a dried electrode plate, and a PTFE coating step of applying polytetrafluoroethylene (PTFE) to the surface of the dried electrode plate by roll transfer to form a PTFE-coated electrode plate. It is desirable to do so. Here, when PTFE is applied after rolling, the PTFE coating liquid penetrates into the conductive core, weakens the strength between the core and the active material, and causes active material peeling. For this reason, it is desirable to provide a rolling / cutting step of rolling the PTFE-coated electrode plate and then cutting it into a predetermined shape to form a hydrogen storage alloy negative electrode.

  At that time, it is more desirable to apply polytetrafluoroethylene (PTFE) dispersed with an anionic water-soluble thickener. This is because, in the present invention, the surface portion of the hydrogen storage alloy negative electrode is defined to have a very small amount of PTFE applied, and therefore it is necessary to use a diluted PTFE solution as the PTFE coating solution. As a result, PTFE is uniformly dispersed in the coating solution, and variations in coating due to sedimentation of PTFE in the coating solution are suppressed.

  In the present invention, a conductive core having a low porosity is used, and a predetermined amount of polytetrafluoroethylene (PTFE) is applied to the surface portion of the hydrogen storage alloy negative electrode to hold the electrolyte solution in the hydrogen storage alloy negative electrode. By setting the amount to a predetermined amount, it is possible to prevent the active material from peeling off and to reduce the reaction resistance, thereby obtaining high output characteristics.

It is sectional drawing which shows the alkaline storage battery of this invention typically.

  Next, embodiments of the present invention will be described in detail below. However, the present invention is not limited to these embodiments, and can be appropriately modified and implemented without departing from the scope of the present invention.

1. Hydrogen storage alloy After mixing metal elements such as lanthanum (La), neodymium (Nd), magnesium (Mg), nickel (Ni), aluminum (Al) so as to have a predetermined molar ratio, these mixtures are mixed with argon gas. This was introduced into a high frequency induction furnace in an atmosphere and melted, and this was cooled to produce an ingot having a composition formula of La _0.2 Nd _0.7 Mg _0.1 Ni _3.7 Al _0.1 , which was designated as a hydrogen storage alloy α1.

  Subsequently, about each obtained hydrogen storage alloy (alpha) 1, melting | fusing point (Tm) was measured using DSC (differential scanning calorimeter). Thereafter, heat treatment was performed for a predetermined time (in this case, 10 hours) at a temperature (Ta = Tm−30 ° C.) lower by 30 ° C. than the melting point (Tm) of these hydrogen storage alloys α1. Thereafter, these hydrogen storage alloys α1 are coarsely pulverized and then mechanically pulverized in an inert gas atmosphere to obtain a hydrogen storage alloy powder having a particle size (D50) of 25 μm at a volume cumulative frequency of 50%. α was produced.

  Next, the crystal structure of the hydrogen storage alloy powder α was identified by a powder X-ray diffraction method using an X-ray diffraction measurement apparatus using a Cu—Kα tube as an X-ray source. In this case, X-ray diffraction measurement was performed at a scan speed of 1 ° / min, a tube voltage of 40 kV, a tube current of 300 mA, a scan step of 1 °, and a measurement angle (2θ) of 20 to 50 °. From the obtained XRD profile, the crystal structure of each hydrogen storage alloy powder α was identified using a JCPDS card chart.

Here, in the composition ratio of the crystal structure, the A ₅ B ₁₉ type structure is a Ce ₅ Co ₁₉ type structure, a Pr ₅ Co ₁₉ type structure and an Sm ₅ Co ₁₉ type structure, and the A ₂ B ₇ type structure is a Ce ₂ Ni ₇ structure. a mold structure, AB ₅ type structure as LaNi ₅ type structure, the ratio the intensity ratio of the strongest intensity values of the intensity values and 42 to 44 ° of the diffraction angle of each structure according to JCPDS, by applying the obtained XRD profile When the composition ratio of each structure is calculated, the A ₅ B ₁₉ type structure is 86%, the A ₂ B ₇ type structure is 11%, the AB ₅ type structure is 3%, and the A ₅ B ₁₉ type structure is mainly used. It turns out to be a phase.

2. Hydrogen storage alloy negative electrode Using the above-described hydrogen storage alloy powder α, the hydrogen storage alloy negative electrode 11 was produced as follows. First, with respect to 100 parts by mass of the obtained hydrogen storage alloy powder α, a water-soluble binder composed of 0.1% by mass of CMC (carboxymethylcellulose) and water (or pure water) is used as a thermoplastic elastomer. Styrene butadiene latex (SBR) and ketjen black as a carbon-based conductive agent were added. Thereafter, these were mixed and kneaded to prepare a hydrogen storage alloy slurry.

  Next, a negative electrode conductive core 11a made of a nickel-plated soft steel porous substrate (punching metal) was prepared. In this case, the punching metal opening ratio ([total area of opening of core body / length of negative electrode × width] × 100) of 28% was defined as negative electrode conductive core β1, and the punching metal was opened. A negative electrode conductive core β2 having a porosity of 25% and a punching metal opening rate of 19% as a negative electrode conductive core β3, and a punching metal porosity of 15%. This was used as the negative electrode conductive core β4.

Thereafter, a hydrogen storage alloy slurry is applied to the negative electrode conductive cores 11a (β1, β3, β4) so as to have a predetermined packing density (for example, 5.0 g / cm ³ ) and dried. After that, it was rolled to a predetermined thickness. Then, it cut | disconnected so that it might become a predetermined dimension (for example, 40 mm x 1000 mm), and produced the hydrogen storage alloy negative electrode 11 (x1-x3), respectively. The negative electrode conductive core β1 was used as the hydrogen storage alloy negative electrode x1, the negative electrode conductive core β3 was used as the hydrogen storage alloy negative electrode x2, and the negative electrode conductive core β4 was used. This was designated as a hydrogen storage alloy negative electrode x3.

Meanwhile, a PTFE coating solution (for example, having a viscosity of 120 mPas) prepared by dispersing PTFE (polytetrafluoroethylene) emulsion with CMC (carboxymethylcellulose) as an anionic water-soluble thickener was prepared. Then, a hydrogen storage alloy slurry was applied to the negative electrode conductive core 11a (β1, β2, β3, β4) so as to have a predetermined filling density (for example, 5.0 g / cm ³ ) and dried. . Thereafter, the PTFE coating solution prepared as described above was applied using a rubber grooved roller so that the PTFE coating amount was 0.09 mg / cm ² .

  After drying, the film was rolled to a predetermined thickness and cut to a predetermined dimension (for example, 40 mm × 1000 mm) to prepare hydrogen storage alloy negative electrodes 11 (a1 to a4). Here, the negative electrode conductive core β1 is used as the hydrogen storage alloy negative electrode a1, the negative electrode conductive core β2 is used as the hydrogen storage alloy negative electrode a2, and the negative electrode conductive core β3 is used. The hydrogen storage alloy negative electrode a3 was used, and the negative electrode conductive core β4 was used as the hydrogen storage alloy negative electrode a4.

  Thereafter, the hydrogen storage alloy negative electrode 11 (a1 to a4) coated with these PTFEs is cut in cross section, and the fluorine (F) on these cut surfaces is observed with an energy dispersive X-ray spectrometer (EDS). did. As a result, it became clear that PTFE was present within the range of (t1-t2) × 0.15 from the surface of the hydrogen storage alloy negative electrode 11 (a1 to a4). In this case, t1 represents the total thickness of the hydrogen storage alloy negative electrode 11 (a1 to a4), and t2 represents the thickness of the negative electrode conductive core 11a (β1, β2, β3, β4).

On the other hand, the strength between the negative electrode conductive core and the active material of the hydrogen storage alloy negative electrodes x1 to x3 and the hydrogen storage alloy negative electrodes a1 to a4 was determined as follows. That is, each of these hydrogen storage alloy negative electrodes 11 was cut to a size of 15 cm × 5 cm, wound around a roll having a radius of 2 cm, and then the winding end was fixed with a tape. Thereafter, the roll was rotated for 5 seconds while applying a force of 0.5 MPa on the negative electrode wound around the roll. Then, the number of times until the active material is peeled off from the core body is obtained by setting such a force of 0.5 MPa and rotation for 5 seconds as one set, and the strength between the conductive core body and the active material is obtained. . And when the strength of the hydrogen storage alloy negative electrode x1 is set to 100 and the strength ratio of the other hydrogen storage alloy negative electrodes x2 to x3 and a1 to a4 is determined as a ratio thereof, the results shown in Table 1 below are obtained. became.

As is clear from the results in Table 1 above, in the hydrogen storage alloy negative electrodes x1 to x3 not coated with PTFE, the strength ratio of the hydrogen storage alloy negative electrode x2 is 79, and the strength ratio of the hydrogen storage alloy negative electrode x3 is 62. It can be seen that the strength ratio between the core and the active material decreases as the core area porosity (%) decreases. On the other hand, in the hydrogen storage alloy negative electrodes a1 to a4 coated so that PTFE is 0.09 mg / cm ² , the porosity (%) of the negative electrode conductive core is 15% to 28%. If it is in the range, it can be seen that the strength ratio between the conductive core and the active material does not change so much. This is because PTFE is fiberized through a drying / rolling process, so that it is possible to improve the strength between the active materials more than the strength reduction due to the decrease in the porosity of the negative electrode conductive core. This is probably because the plate strength was maintained.

3. Nickel positive electrode On the other hand, a porous nickel sintered substrate having a porosity of about 85% is immersed in a mixed aqueous solution of nickel nitrate and cobalt nitrate having a specific gravity of 1.75, and a nickel salt is placed in the pores of the porous nickel sintered substrate. And cobalt salts were retained. Thereafter, the porous nickel sintered substrate was immersed in a 25% by mass sodium hydroxide (NaOH) aqueous solution to convert the nickel salt and the cobalt salt into nickel hydroxide and cobalt hydroxide, respectively.

Next, after sufficiently washing with water to remove the alkaline solution, drying was performed, and the active material mainly composed of nickel hydroxide was filled into the pores of the porous nickel sintered substrate. Such an active material filling operation is repeated a predetermined number of times (for example, 6 times) so that the filling density of the active material mainly composed of nickel hydroxide in the pores of the porous sintered substrate becomes 2.5 g / cm ^3. Filled. Then, after making it dry at room temperature, it cut | disconnected to the predetermined dimension and the nickel positive electrode 12 was produced.

4). Nickel-hydrogen storage battery Thereafter, the hydrogen storage alloy negative electrode 11 (x1 to x3) (a1 to a4) and the nickel positive electrode 12 produced as described above are used, and a non-woven fabric that is sulfonated between them is formed. A spiral electrode group was prepared by winding the separator 13 in a spiral shape. The core exposed portion 11c of the hydrogen storage alloy negative electrode 11 is exposed at the lower part of the spiral electrode group thus fabricated, and the core exposed part 12c of the nickel positive electrode 12 is exposed at the upper portion thereof. ing. Next, the negative electrode current collector 14 is welded to the core exposed portion 11c exposed at the lower end surface of the obtained spiral electrode group, and the core exposed portion 12c of the nickel positive electrode 12 exposed at the upper end surface of the spiral electrode group. A positive electrode current collector 15 was welded onto the electrode body to obtain an electrode body.

  Next, after the obtained electrode body is housed in a bottomed cylindrical outer can 16 in which iron is nickel-plated (the outer surface of the bottom surface becomes a negative electrode external terminal) 16, the negative electrode current collector 14 is attached to the outer can 16. Welded to the inner bottom. On the other hand, the current collecting lead portion 15a extending from the positive electrode current collector 15 was welded to a sealing plate 17a constituting the bottom portion of the sealing body 17 which also served as a positive electrode terminal and was fitted with an insulating gasket 18 on the outer peripheral portion. The sealing body 17 is provided with a positive electrode cap 17b, and a pressure valve including a valve body 17c and a spring 17d which are deformed when a predetermined pressure is reached is disposed in the positive electrode cap 17b.

  Next, after forming the annular groove portion 16 a on the upper outer peripheral portion of the outer can 16, the electrolytic solution was injected, and the outer peripheral portion of the sealing body 17 was mounted on the annular groove portion 16 a formed on the upper portion of the outer can 16. An insulating gasket 18 was placed. Then, the nickel-hydrogen storage battery 10 (X1-X3) (A1-A4) was produced by caulking the opening edge 16b of the armored can 16. In this case, an alkaline electrolyte composed of a 30% by mass potassium hydroxide (KOH) aqueous solution in the outer can 16 is 2.5 g (2.5 g / Ah) or 2.8 g (2.8 g) per battery capacity (Ah). / Ah) to produce nickel-hydrogen storage batteries 10 (X1 to X3) (A1 to A4).

  Here, the battery using the negative electrode x1 is referred to as a battery X1, the battery using the negative electrode x2 is referred to as the battery X2, and the battery using the negative electrode x3 is referred to as the battery X3. A battery using the negative electrode a1 is referred to as a battery A1, a battery using the negative electrode a2 is referred to as a battery A2, a battery using the negative electrode a3 is referred to as a battery A3, and a battery using the negative electrode a4 is referred to as a battery A4.

5). Battery Test (1) Activation Next, the batteries X1 to X3 and A1 to A4 produced as described above were activated as follows. In this case, after the battery is manufactured, the battery is left until the battery voltage reaches 60% of the peak voltage when left, and then at a temperature atmosphere of 25 ° C., the current of 1 It is charged to 120% of SOC (State Of Charge). Charge and rest for 1 hour in a 25 ° C. temperature atmosphere. Then, after being left for 24 hours in a temperature atmosphere of 70 ° C., a cycle of discharging in a temperature atmosphere of 45 ° C. with a discharge current of 1 It until the battery voltage reaches 0.3 V was repeated two times, and each of these batteries X1 -X3, A1-A4 were activated.

(2) Measurement of electrolyte amount ratio After activation as described above, each of these batteries X1 to X3 and A1 to A4 is replaced with a hydrogen storage alloy negative electrode 11, a nickel positive electrode 12, a separator 13, and current collectors 14 and 15. And it disassembled into each structural member such as the outer can 16. Next, the amount of change in mass immediately after disassembly and after vacuum drying, that is, the amount of electrolyte solution held by each component was measured. Thereafter, when the ratio of the amount of electrolyte (X) retained by the hydrogen storage alloy negative electrode 11 to the total amount of electrolyte (Y), that is, the liquid retention (X / Y), was obtained as shown in Table 2 below. It became a result.

(3) Output characteristic evaluation Moreover, after activating as mentioned above, each of these batteries X1 to X3 and A1 to A4 is SOC (State Of Charge) at a charging current of 1 It in a temperature atmosphere of 25 ° C. ) To 50%, and then rest for 1 hour in a temperature atmosphere of 25 ° C. Next, the battery is charged at an arbitrary charging rate for 20 seconds in a temperature atmosphere of −10 ° C., and then rested in a temperature atmosphere of −10 ° C. for 30 minutes. Then, after discharging at an arbitrary discharge rate for 10 seconds in a temperature atmosphere of −10 ° C., it is paused for 30 minutes in a temperature atmosphere of 25 ° C. In such a temperature atmosphere of −10 ° C., charging for 20 seconds at an arbitrary charging rate, a pause for 30 minutes, discharging for 10 seconds at an arbitrary discharge rate, and a pause for 30 minutes in a temperature atmosphere at 25 ° C. were repeated.

  In this case, an arbitrary charging rate increases charging current in the order of 0.8 It → 1.7 It → 2.5 It → 3.3 It → 4.2 It, and an arbitrary discharging rate is 1.7 It → 3.3 It. → The discharge current is increased in the order of 5.0 It → 6.7 It → 8.3 It, and the battery voltage (V) of each of the batteries X1 to X3 and A1 to A4 at each discharge rate when 10 seconds elapses for each current Each was measured. Here, as an indicator of discharge characteristics (assist output characteristics), 0.9 V current on the discharge VI plot approximate curve was obtained as -10 ° C. assist output. In the calculated -10 ° C assist output, the -10 ° C assist output of the battery X1 is used as a reference (100), and the relative ratio thereof is calculated as the -10 ° C assist output ratio (vs. battery X1). The result was as shown.

(4) Measurement of oxygen concentration (oxidation index) Next, the oxygen concentration as an oxidation index was measured as follows. In this case, after activation as described above, each of the batteries X1 to X3 and A1 to A4 was disassembled and decomposed to peel the active material from the negative electrode. Thereafter, ultrasonic cleaning was performed to remove components other than the hydrogen storage alloy powder such as additives, and then vacuum drying was performed to measure the oxygen concentration of the hydrogen storage alloy. Then, in the obtained oxygen concentration, when the oxygen concentration of the battery X1 was used as the reference (100) and the relative ratio thereof was calculated as the oxidation index (vs. the battery X1), the results shown in Table 2 below were obtained. .

  From the results in Table 2 above, the following became clear. That is, in the batteries X2 and X3 using the negative electrodes x2 and x3 having a low porosity of the negative electrode conductive core 11a and not coated with PTFE, as described above, the electrode plate strength (the conductive core 11a and It can be seen that the strength between the active materials is decreased, the retention rate of the electrolytic solution in the negative electrode is increased, and the output reduction and the oxygen concentration (oxidation) are increased. This is because when the electrolytic solution is injected, the active material is peeled off, and the peeled portion of the active material causes a decrease in output. It is considered that the retention rate of the electrolytic solution at 11 increased and the oxidation progressed (the oxygen concentration increased).

  On the other hand, in the batteries A2 to A4 using the negative electrode 11 (a2 to a4) coated with PTFE, even if the porosity of the negative electrode conductive core 11a is as low as 15 to 25%, the negative electrode 11 (a2 It can be seen that the retention rate of the electrolytic solution in ~ a4) tends to decrease, and both improvement in output (output characteristics 100% or more) and improvement in corrosion resistance (oxidation index 100% or less) are compatible. In this case, even when PTFE is applied like the negative electrode a1, it can be seen that the output is reduced when the porosity of the negative electrode conductive core 11a is 28%. This is presumably because the current collecting property of the negative electrode conductive core 11a was reduced when the porosity of the negative electrode conductive core 11a was increased to 28%. From this, it can be said that the porosity of the negative electrode conductive core 11a is desirably 15 to 25%.

5). Examination of PTFE Application Location and Application Amount Next, the PTFE application location and application amount of the hydrogen storage alloy negative electrode 11 were examined. Therefore, a negative electrode conductive core β2 (having a punching metal opening rate of 25%) and a hydrogen storage alloy slurry so as to have a predetermined packing density (for example, 5.0 g / cm ³ ). was Nurigi, dried, the PTFE coating solution prepared as above using grooved rollers made of rubber, 0.02 mg / cm ² is applied amount of PTFE, 0.11 mg / cm ^2, And 0.16 mg / cm ² . After drying, the film was rolled to a predetermined thickness and cut to a predetermined dimension (for example, 40 mm × 1000 mm) to produce hydrogen storage alloy negative electrodes 11 (b, c, d). Incidentally, those coating amount of PTFE is 0.02 mg / cm ² and a negative electrode b, and that the coating amount of PTFE is 0.11 mg / cm ² and a negative electrode c, the coating amount of PTFE is 0.16 mg / cm ^The one that would be ² was designated as negative electrode d.

On the other hand, a negative electrode conductive core β2 (having a punching metal hole area ratio of 25%) and a hydrogen storage alloy slurry with a predetermined filling density (for example, 5.0 g / cm ³ ). After being coated and dried, it was rolled to a predetermined thickness. Then, each negative electrode of the rolling, the PTFE coating solution prepared as above using grooved rollers made of rubber, 0.02 mg / cm ² is applied amount of PTFE, 0.11 mg / cm ^2, and 0 .16 mg / cm ² was applied and dried, and then cut to a predetermined size (for example, 40 mm × 1000 mm) to prepare hydrogen storage alloy negative electrodes 11 (e, f, g), respectively. . Incidentally, those coating amount of PTFE is 0.02 mg / cm ² and a negative electrode e, those coating amount of PTFE is 0.11 mg / cm ² and a negative electrode f, the coating amount of PTFE is 0.16 mg / cm ^The one to be ² was designated as negative electrode g.

Thereafter, in the same manner as described above, these hydrogen storage alloy negative electrodes 11 (b to g) were cut in cross-section, and fluorine (F) on these cut surfaces was obtained by an energy dispersive X-ray spectrometer (EDS). Observed. As a result, it became clear that PTFE was present within the range of (t1-t2) × 0.15 from the surface of the hydrogen storage alloy negative electrode 11 (b to g). On the other hand, when the strength between the negative electrode conductive core 11a and the active material of the hydrogen storage alloy negative electrodes b to g was determined in the same manner as described above, the results shown in Table 3 below were obtained. Also in this case, when the strength of the hydrogen storage alloy negative electrode x1 was set to 100 and the strength ratio of the other hydrogen storage alloy negative electrodes b to g was determined as a ratio thereof, the results shown in Table 3 below were obtained. .

As is clear from the results of Table 3 above, in the hydrogen storage alloy negative electrode e, f, g coated with PTFE after rolling, the strength ratio of the hydrogen storage alloy negative electrode e is 61, and the hydrogen storage alloy negative electrode f, g It can be seen that the strength ratio is 72, 71, and the strength ratio between the negative electrode conductive core 11a and the active material is reduced. On the other hand, in the hydrogen storage alloy negative electrodes b, c and d coated with PTFE before rolling, the strength ratio of the hydrogen storage alloy negative electrode b is 115 and the strength ratio of the hydrogen storage alloy negative electrodes c and d is 121. It can be seen that the strength ratio between the core and the active material is remarkably improved.
This is presumably because when PTFE was applied after rolling, the PTFE coating solution penetrated into the core and caused the active material to peel off. On the other hand, when PTFE is applied before rolling, the PTFE coating solution is absorbed in the active material and rolled after drying, so that the active material is not peeled off and the strength is not reduced. Conceivable.

  Subsequently, nickel-hydrogen storage batteries B, C, and D were respectively produced using negative electrodes b, c, and d formed by applying PTFE before rolling. In this case, the battery B was used as the battery B, the battery C was used as the negative electrode c, and the battery D was used as the negative electrode d. A battery using the negative electrode b was designated as a battery B, a battery using the negative electrode c was designated as a battery C, and a battery using the negative electrode d was designated as a battery D.

Then, after activating each of the batteries B, C, D in the same manner as described above, the batteries B, C, D are disassembled into the constituent members in the same manner as described above, and the hydrogen storage alloy negative electrode 11 with respect to the total electrolyte amount (Y) is held. When the ratio of the electrolyte amount (X), that is, the liquid retention (X / Y) was determined, the results shown in Table 4 below were obtained. In addition, after activation, the -10 ° C assist output was obtained in the same manner as described above, and in the obtained -10 ° C assist output, the -10 ° C assist output of the battery X1 described above was used as the reference (100), and the relative ratio thereof was determined. When calculated as the −10 ° C. assist output ratio (vs. battery X1), the results shown in Table 4 below were obtained. Further, after activation, the oxygen concentration is measured in the same manner as described above, and the oxygen concentration of the battery X1 described above is used as a reference (100) and the relative ratio thereof is calculated as an oxidation index (vs. battery X1). The results shown in 4 were obtained. Table 4 below also shows the results of the battery A2 described above.

From the results in Table 4 above, the following became clear. That is, it can be seen that in the battery D using the negative electrode d coated with PTFE so that the coating amount is 0.16 mg / cm ² , the output characteristics are deteriorated. This is presumably because the effect of increasing the reaction resistance by applying PTFE is larger than the effect of decreasing the reaction resistance by reducing the opening ratio of the core. On the other hand, in the batteries B, A2, and C using the negative electrodes b, a2, and c coated with PTFE so that the coating amount of PTFE is 0.02 to 0.11 mg / cm ² , the output characteristics are improved. I understand that. From this, it can be seen that the amount of PTFE applied is preferably 0.02 to 0.11 mg / cm ² .

As described above, in the present invention, a core having a lower porosity than the conventional porosity (28% or more) is used, and polytetrafluoroethylene (PTFE) is added to the surface of the hydrogen storage alloy negative electrode to a value of 0.1. By applying only 02 to 0.11 mg / cm ^2, it has become possible to exhibit the effect of lowering the retention rate of the electrolytic solution in the hydrogen storage alloy negative electrode than the conventional range.
In this case, if the retention rate of the electrolyte in the hydrogen storage alloy negative electrode is reduced, the three-phase interface (the interface between the hydrogen storage alloy negative electrode, the electrolyte, and the space) decreases, so the hydrogen storage alloy used in the hydrogen storage alloy negative electrode Is preferably an alloy containing an A ₅ B ₁₉ type structural phase mainly composed of rare earth, nickel, and magnesium.

This is because the A ₅ B ₁₉ type structure has the AB ₂ type structure and the AB ₅ type structure stacked in a cycle of three layers, and the ratio of nickel (Ni) per unit crystal lattice is higher than that of the A ₂ B ₇ type structure. It can be increased. And if the ratio of nickel (Ni) per unit crystal lattice increases, it becomes possible to increase the active sites that promote the adsorption of hydrogen molecules and the dissociation into hydrogen atoms, This is because high output characteristics can be improved.

  In the embodiment described above, polytetrafluoroethylene (PTFE) is applied to the surface portion of the hydrogen storage alloy negative electrode. However, other fluororesins other than polytetrafluoroethylene (PTFE), such as FEP, etc. You may make it apply | coat. Moreover, in embodiment mentioned above, although the example using CMC (carboxymethylcellulose) as an anionic water-soluble thickener was demonstrated, as anionic water-soluble thickener other than CMC (carboxymethylcellulose), polycarboxylic acid and Anionic water-soluble polymers such as polyacrylic acid copolymers and their ammonium salts, and copolymers of vinyl monomers and acrylamide hydrophilic monomers may be used. Furthermore, in the above-described embodiment, an example in which ketjen black is added as a carbon-based conductive agent has been described. However, carbon nanomaterials such as activated carbon and carbon nanotubes are added as a carbon-based conductive agent other than ketjen black. You may make it do.

DESCRIPTION OF SYMBOLS 11 ... Hydrogen storage alloy negative electrode, 11a ... Electroconductive core for negative electrodes, 11b ... Active material layer, 11c ... Core body exposed part, 12 ... Nickel positive electrode, 12c ... Core body exposed part, 13 ... Separator, 14 ... Negative electrode current collection 15, positive electrode current collector, 15 a, positive electrode lead, 16, outer can, 16 a, annular groove, 16 b, opening edge, 17, sealing body, 17 a, sealing plate, 17 b, positive electrode cap, 17 c, valve plate , 17d ... Spring, 18 ... Insulating gasket

Claims (6)

A hydrogen storage alloy negative electrode using a hydrogen storage alloy as a negative electrode active material, and a positive electrode using nickel hydroxide as a main positive electrode active material, and an electrode group wound in a spiral through a separator that separates both electrodes; An alkaline storage battery containing an alkaline electrolyte in an outer can,
The porosity of the conductive core used for the hydrogen storage alloy negative electrode is 15% to 25%, and polytetrafluoroethylene (PTFE) is 0.02 mg / cm ^{2 to} 0 on the surface of the hydrogen storage alloy negative electrode. Only 11 mg / cm ^{2 is} applied,
An alkaline storage battery, wherein a retention rate of the electrolytic solution held by the hydrogen storage alloy negative electrode with respect to a total amount of the electrolytic solution is 23% to 29%.   The surface portion of the hydrogen storage alloy negative electrode is (t1−) from the surface of the hydrogen storage alloy electrode when the thickness of the hydrogen storage alloy negative electrode is t1, and the thickness of the conductive core of the hydrogen storage alloy negative electrode is t2. The alkaline storage battery according to claim 1, wherein the alkaline storage battery is within a range of t2) x 0.15. The hydrogen storage alloy is a hydrogen storage alloy composed of an A component composed of an element including at least a rare earth element and magnesium and a B component composed of an element including at least nickel, and the alloy main phase is an A ₅ B ₁₉ type structure. The alkaline storage battery according to claim 1 or 2, characterized in that Using a hydrogen storage alloy negative electrode formed by applying a hydrogen storage alloy slurry using a hydrogen storage alloy as a negative electrode active material to a conductive core, and a positive electrode using nickel hydroxide as a main positive electrode active material. A method for producing an alkaline storage battery in which an electrode group formed by winding in a spiral shape through a separator that isolates a battery is housed in an outer can together with an alkaline electrolyte,
A slurry application step of applying the hydrogen storage alloy slurry to a conductive core to form a slurry-coated electrode plate;
A drying step of drying the slurry-coated electrode plate to form a dry electrode plate;
A method for producing an alkaline storage battery, comprising: a polytetrafluoroethylene coating step in which polytetrafluoroethylene (PTFE) is coated on a surface of the dry electrode plate by roll transfer to form a polytetrafluoroethylene-coated electrode plate. .   5. The method for producing an alkaline storage battery according to claim 4, further comprising a rolling / cutting step of rolling the polytetrafluoroethylene-coated electrode plate into a predetermined shape to form a hydrogen storage alloy negative electrode.   The method for producing an alkaline storage battery according to claim 4 or 5, wherein the polytetrafluoroethylene (PTFE) is dispersed and applied with an anionic water-soluble thickener.

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